Up to half of Czech population may already have COVID-19 antibodies, largescale study finds

Based on the number of positive PCR and antigen test results, around 17 percent of the Czech population has so far been infected with COVID-19. However, according to the results of the first phase of a study conducted by the RECETOX research centre at the Masaryk University in Brno, around half of the adult Czech population may in fact already have been infected with the virus and developed antibodies.

Illustrative photo: Bill Dickinson,  Flickr,  CC BY-NC 2.0

The Czech Republic went from being one of the most successful countries in tackling the spread of COVID-19 in the intial spring 2020 period to one of the worst in Europe in the subsequent “second wave” that hit the country during the autumn and winter.

Experts have long been speculating about how much of the Czech population may have passed under the radar either by having no symptoms or not getting tested.

The answer to that question may have been provided by the results of an antibodies study conducted by the RECETOX research centre, which was able to test a large number of volunteers from among the clientelle of the health insurance company of the Ministry of Interior (Zdravotní pojišťovna Ministerstva vnitra).

Vojtěch Thon | Photo:  ČT24

Professor Vojtěch Thon, who led the university research team, spoke to Czech Television on Wednesday.

“We have a test which records the specificity of antibodies, in other words - whether one has encountered the virus in the past. We were able to gather a significant sample pool, close to 30,000 people.

“What is also important is that this was a continuous study, so we were able to detect the dynamic of the spread. We managed to capture the whole [second] wave of the epidemic, from the initial period, when the circulation of the virus was minimal, until the turn of 2020/2021, when the viral load was enourmous. We see that these specific antibodies appear among all age groups within the population.”

Illustrative photo: Michaela Danelová,  Czech Radio

The study’s results show that a rapid increase in seropositivity occurred within the Czech population from the autumn of 2020 to the early months of 2021. While in October and November 2020 just 28 percent of volunteers had antibodies, in December 2020 and January 2021 it was 43 percent and in March 2021 the number reached 51 percent.

Another interesting discovery was that 16 percent of the volunteers who had previously been infected with the the SARS-CoV-2 virus, but then recovered, did not have any antibodies.

Illustrative photo: Martin Sanchez,  Unsplash,  CC0 1.0

Meanwhile, around a third the test subjects who did have antibodies had not noticed any COVID-19 symptoms. In fact, 28 percent of the volunteers who did test positive for antibodies had not even taken a single PCR test before the study, Professor Thon told Czech Television.

“This is very good news, because it means that, as a society, we have already encountered the virus and are able to react to repeated infections with an immunity system that is no longer naive [to the virus].“

Illustrative photo: Lucie Fürstová,  Czech Radio

Authors warn that the study should not be considered as representative, because not all of the volunteers were selected randomly. It is possible that some of the tested subjects volunteered, because they had noticed health issues and wanted to find out whether they had been infected with the virus.

Furthermore, some parts of the population were overrepresented in the study, especially people in their middle age who are normally more at risk of catching the virus due to frequent contact with others. Pensioners living in care homes were not tested at all.

Illustrative photo: Jernej Furman,  Flickr,  CC BY 2.0

The study was conducted with support from epidemiologists at Univeristy College London, the Prague office of the World Health Organisation and the Czech Institute of Health Information and Statistics.

Research will continue in two more phases. The second phase runs from March to September 2021 and is measuring the level of antibodies among volunteers during the mass vaccination of the population that is taking place during this spring and summer. The subsequent third  phase will measure the retention, or possible decline, of IgG antibodies among individuals who either recovered from the virus or were vaccinated.